Acoustic observations of suspended particulate matter in the ocean

• Published in: Nature (London) 1975-01, Vol.254 (5499), p.413-415
• Main Authors: Proni, J R, Rona, D C, Lauter, CA, Sellers, R L
• Format: Article
• Language: English
• Subjects: Marine
• ISSN: 0028-0836
• DOI: 10.1038/254413a0

During field trials of a 20-k Hz LODAR echo-sounding system, which has a downward-looking acoustic beam of 12{degree} by 18{degree} and a pulse duration of 2.2 ms, the feasibility of acoustic surveys of suspended sediments was investigated. Acoustic records were coincident with visual sightings of suspended sediment down-current of a working dredge. The observed acoustic 'cloud' cannot be accounted for by temp anomalies, a package of contaminated bay water, large biological reflectors or microbubbles produced by organic processes in the sediment and released by dredging operations. The expected effects of temp and tides on the suspended sediments were observed. The authors consider how particles with diams that may be 1-100 {mu}m can reflect detectable sound signals at 20kHz. It is suggested that the sediment cloud may have regions of relatively high particulate conc which are detectable but not resolvable using this acoustic system.